不同林龄油茶人工林土壤-叶片碳氮磷生态化学计量特征

油茶是世界四大木本油料植物之一,在我国有着2000多年的栽培和利用历史。碳(C)、氮(N)、磷(P)化学计量元素是近年来研究的热点,通过C、N、P化学计量我们可以深入了解植物-土壤间元素相互关系,并能揭示土壤养分限制状况。为了解油茶人工林生态系统C、N、P化学计量特征及油茶人工林养分元素限制因素,以长江中下游油茶适宜栽培区湖南、江西和湖北三省油茶林为研究对象,采用空间代替时间的研究方法,在区域尺度上随机选择32个典型油茶人工林并分为4个林龄组(9年低龄林;9—20年高产林;21—60年低产林; 60年生产退化林)。测定油茶人工林土壤与油茶叶片中的C、N、P含量并分析其化学计量特征。研究结果表明:(1)随林龄增加,油茶人工林土壤有机碳(SOC)和全氮(TN)含量增大,而土壤全磷(TP)和速效/kg和5.43 mg P在一定的林龄(60 a)内具有增加的趋势。(2)随林龄增加,油茶人工林叶片C含量无显著变化,N、P含量降低,叶片的C、/kg、11.66—15.46 g增大。此外,叶片N∶P阈值分析发现,叶片N∶P比在四个林龄段均16。(3)相关分析结果表明,油茶人工林土壤SOC和TN具有显著正相关,油茶叶片N和P具有显著正相关。同时,叶片N含量与土壤TN无相关性,而油茶叶片P含量与土壤Olsen-P显著正相关。油茶人工林土壤化学计量C∶N、C∶P和N∶P与叶片C∶N、C∶P呈显著正相关,以及叶片N∶P与土壤C∶P、N∶P呈显著正相关(P0.05)。由以上可见,油茶人工林土壤主要受P养分限制,且随林龄增加,P限制增加。此外油茶叶片N、P吸收具有协同效应,且油茶叶片与土壤元素存在广泛的计量耦合关系。本研究综合分析油茶林叶片与土壤的C、N、P计量特征及其关系,有助于全面系统的揭示油茶人工林生态系统的养分状况,对油茶林高效培育、养分补充或退化林诊断等具有指导意义。

The stoichiometry characteristics of soil and plant carbon, nitrogen, and phosphorus in different stand ages in Camellia oleifera plantation

Camellia oleifera is one of the four woody oil plants in the world and it has been cultivated for over 2000 years. Recent studies have increasingly focused on carbon (C), nitrogen (N), and phosphorus (P) stoichiometry, which reflects the interaction of vegetation and soil and reveals soil nutrient limitations. To understand the C, N, and P stoichiometric characteristics of C. oleifera plantations and the factors that limit the growth of C. oleifera during stand development, we conducted a field experiment to investigate the plant leaf and soil C, N, and P contents and their stoichiometric ratios in different stand ages in Hunan, Jiangxi, and Hubei provinces, in China. We randomly selected 32 C. oleifera plantations across the subtropical region. Using space instead of time, all C. oleifera plantations were classified into four stand ages:under 9 years old, 9-20 years old, 20-60 years old, and over 60 years old. The results showed that:(1) the soil organic carbon (SOC) and total N (TN) contents of C. oleifera plantations increased with the increasing stand age, while the total P (TP) and Olsen-P contents did not significantly change during stand development and were always maintained at a low level (average values of 0.36 g/kg and 5.43 g/kg, respectively); soil stoichiometry (C:N, C:P, and N:P ratios) showed an increasing trend in under 60 year-old forests; (2) the leaf C content did not vary significantly with stand age, while the N and P contents decreased with the increase of stand age. Leaf C, N, and P contents were 498-506 g/kg, 11.66-15.46 g/kg, and 0.66-0.95 g/kg in all tested C. oleifera plantations, respectively. Leaf C:N, C:P, and N:P ratios increased with the increasing stand age. The leaf N:P ratio was over 16 in all stand ages. A correlation analysis showed a significantly positive relationship between SOC and soil TN, and a significantly positive relationship between leaf N and P contents. The leaf P content was positively correlated with soil TP and Olsen-P contents, while the leaf N content was not correlated with soil TN content. The correlation analysis also showed the significantly positive relationships between leaf and soil C, N, and P stoichiometric ratios. In summary, C. oleifera plantations were mainly restricted by P, and P limitation increased with stand age. In addition, N and P acquisition had a synergistic effect in C. oleifera, and there was a broad quantitative coupling relationship between the leaves of C. oleifera and soil elements. We suggest that the input of P and the balance of soil nutrients should be considered in the management of C. oleifera plantations. Our study systematically analyzed the stoichiometric characteristics of plant and soil C, N, and P in different stand ages and revealed the nutrient status of C. oleifera plantations.